In modern telephone stations, for example, a large number of magazines containing circuit boards are used, air flowing between the boards to take away the heat generated by the circuit board components. The air can be caused to flow by convection, a draft thus occurring as warm air rises. Forced cooling may also be used, and implemented by mechanical means such as a fan which preferably reinforces the convection draft.
In such an arrangement, a problem may exist that the cooling of certain circuit boards may be insufficient, even if the total air flow through a magazine is nominally large enough. This may result from the fact that whereas the air flows passing close to all the circuit boards are substantially equal, the boards may generate different amounts of heat.
The risk of components or certain boards becoming too hot, and thus being damaged, is especially large if the magazines are placed in a closed cabinet. Further, if a fan is used to increase the air flow, it must be powerful enough to insure that the boards generating the most heat will be sufficiently cooled. Such a fan requires energy as well as space, and can also cause troublesome noise.